This investigation involves the secondary analysis of several large-scale data sets centering on, or containing information relevant to, the self-concept. Our current explorations focus on four relatively unexplored issues in self-concept research: mattering; transient depersonalization; self-concept instability; and self-presentation. Mattering refers to the individual's conviction that he is an object of importance or concern to another. Four data sets were analyzed to explore the adolescent's conviction that he mattered to his parents. Mattering proved to be significantly related to self-esteem, depressive affect, anxiety, negative affective states, and juvenile delinquency. Mattering was higher among upper class adolescents and only children. Transient depersonalization refers to the feeling of being temporarily estranged from the self -- of looking upon the self as a stranger, with accompanying feelings of unreality. A five-item depersonalization scale (Cronbach's Alpha of .66) was studied in a sample of 1988 school children. Depersonalization is found to appear when the individual violates his self-expectations or under certain interpersonal conditions. It is significantly associated with self-esteem, self-concept stability, public self-consciousness, private self-consciousness, self-presentation and daydreaming. Between the ages of 12-16, girls' depersonalization scores are significantly higher than boys; no consistent gender differences appear at other ages.